Lubrication involves the process of friction reduction, accomplished by maintaining a film of a lubricant between surfaces which are moving with respect to each other. The lubricant prevents contact of the moving surfaces, thus greatly lowering the coefficient of friction. In addition to this function, the lubricant also can be called upon to perform heat removal, containment of contaminants, and other important functions. Additives have been developed to establish or enhance various properties of lubricants. Various additives which are used include viscosity improvers, detergents, dispersants, antioxidants, extreme pressure additives, and corrosion inhibitors.
Fuel efficiency is one of the most challenging areas in today's lubricant development. Friction modifiers are widely used in lubricant formulations. Organic molybdenum compounds are very effective friction modifiers. However, corrosion is one of the main factors that limit the broad use of high concentrations of organic molybdenum compounds.
There are two commonly used organic molybdenum compound friction modifiers, namely molybdenum dialkyldithiocarbamate (MoDTC) and molybdenum dialkyldithiophosphate (MoDTP). It is also known that these molybdenum compounds contribute to copper corrosion. See, for example, EP 0316610A1 and R. T. Vanderbilt literatures that indicate in some formulations, the presence of Molyvan™ 822 (MoDTC) and Molyvan™ L (MoDTP) contribute to copper corrosion which is detrimental to some diesel engines. The corrosion issue is one of the key factors that limit the use of high concentration of organic molybdenum compounds in formulating high fuel economy lubricants.
Despite advances in lubricant oil formulation technology, there exists a need for an engine oil lubricant that effectively improves corrosion protection and friction coefficient in order to improve engine durability and fuel efficiency.